Npgrj_nn_1631 180..187

Neural crest cells (NCCs) can adopt different neuronal fates. In NCCs, neurogenin-2 promotes sensory specification but does not specify different subclasses of sensory neurons. Understanding the gene cascades that direct Trk gene activation may reveal mechanisms generating sensory diversity, because different Trks are expressed in different sensory neuron subpopulations. Here we show in chick and mouse that the Runt transcription factor Runx1 promotes axonal growth, is selectively expressed in neural crest–derived TrkA1 sensory neurons and mediates TrkA transactivation in migratory NCCs. Inhibition of Runt activity depletes TrkA expression and leads to neuronal death. Moreover, Runx1 overexpression is incompatible with multipotency in the migratory neural crest but does not induce expression of pan-neuronal genes. Instead, Runx1-induced neuronal differentiation depends on an existing neurogenin2 proneural gene program. Our data show that Runx1 directs, in a context-dependent manner, key aspects of the establishment of the TrkA1 nociceptive subclass of neurons.